Engines operating with a variable number of active or deactivated cylinders, also referred to as variable displacement engines (or VDE), may be used to increase fuel economy while optionally maintaining an overall exhaust mixture air-fuel ratio about stoichiometry. In some examples, half of an engine's cylinders may be disabled during selected conditions, where the selected conditions can be defined by parameters such as a speed/load window, vehicle speed, etc. In still other examples, cylinders may be individually and selectively deactivated.
A VDE control system may disable selected cylinders through the control of a plurality of cylinder valve deactivators that affect the operation of the cylinder's intake and exhaust valves. Various mechanisms may be used to change the state of cylinder valves from an active state, where they are able to lift, to a deactivated state, where they cannot be lifted. One example of a cylinder deactivation mechanism includes electrically actuated latches coupled to rocker arm assemblies to implement zero valve lift and cylinder deactivation. Therein, valve operation may be adjusted via a rocker arm assembly that includes a latch pin mounted on a rocker arm, the latch pin electrically actuated via a solenoid. Movement of the latch pin into or out of the rocker arm assembly affects an activation state of the corresponding valve. Since the valves control the flow of air and fuel into an engine cylinder for combustion, the position and state of the valves may be required at an engine start so that fueling and spark timing can be accurately coordinated to obtain reliable combustion and low emissions. For example, precise and timely knowledge of the state of each valve of a first cylinder to receive fuel may enable sufficient combustion torque to be generated to overcome a cylinder air spring effect and start spinning the engine.
One example of valve position sensing is shown by Nielsen et al. in U.S. Pat. No. 9,284,859. Therein, a linear variable differential transformer (LVDT) is coupled to the valve stem to monitor the linear motion of the stem via magnetic properties. A signal representative of the monitored motion is compared to a sensed crankshaft position to determine the valve position.
However, the inventors herein have identified potential issues with such an approach. As one example, the approach relies on costly sensors and transformers. Also, the sensors and transformers may be prone to degradation and may need to be periodically diagnosed. Furthermore, in addition to the state of the cylinder valve being unknown, the state of the rocker arm coupled to the valve, and configured to selectively deactivate the valve, may also be unknown at engine crank. Therefore, an engine controller may not have an accurate estimate of how much air the engine will intake, resulting in inaccurate control of engine operation. For example, if an intake valve does not open as expected, air is not inducted into the corresponding cylinder, preventing that cylinder from creating any torque, increasing a duration of engine cranking. As another example, if an exhaust valve does not open as expected, combustion gases do not leave the corresponding cylinder, causing a high pressure blow down event into the intake, which may result in customer concern due to noise, vibration, and harshness (NVH) and/or engine degradation.
The inventors herein have recognized that the electrically actuated latch pin valve deactivation mechanism provides an opportunity for setting the cylinder valves to a desired state at engine crank, even if a current valve state and rocker arm state are unknown. In one example, valve state can be determined by a method comprising: at key-on, energizing a solenoid of a valve deactivation mechanism of a cylinder valve; and re-energizing the solenoid after a threshold duration, greater than a valve duration, has elapsed. In this way, valve state at engine start can be accurately set without requiring costly sensors or camshaft sensing.
As an example, an engine system may include cylinders having valves that are selectively deactivatable via a cylinder deactivation mechanism that includes a latch pin mounted on a rocker arm assembly. An engine controller can apply a voltage pulse to energize a solenoid coupled to the latch pin, the energization changing the state of the latch pin when the rocker arm is unloaded. For example, if the latch pin was engaged to the rocker arm assembly, the energization of the solenoid with a first polarity moves the latch pin out of the rocker arm assembly, thereby deactivating the corresponding cylinder valve. Alternatively, if the latch pin was disengaged from the rocker arm assembly, the energization of the solenoid with a second polarity moves the latch pin in to the rocker arm assembly, thereby reactivating the corresponding cylinder valve. The intake valve latch pin cannot move during an intake stroke, when the associated intake cam is on the cam lobe and an intake valve rocker arm is loaded. Likewise, the exhaust valve latch pin cannot move during the exhaust stroke, when the associated exhaust cam is on the lobe and an exhaust valve rocker arm is loaded. Consequently, after a maximum valve duration, any valve that was open will be closed and the latch pin mechanism can be cycled. For example, on a 4 cycle engine, the maximum valve duration may be 200 to 280 degrees out of 720 degrees, such that after 280 degrees of engine rotation, the latch pin mechanism can be re-energized. Consequently, the controller can actuate the solenoids coupled to each cylinder valve to set the corresponding valves to a desired state at engine start (or the preceding shutdown). After a threshold crankshaft rotation corresponding to the maximum valve duration has elapsed, the solenoids can be re-energized to actuate the latch pin so as to set the valve to the desired state. The rocker arms that were previously loaded, where the latch pin did not move, will now be unloaded, enabling the latch pin to move.
In this way, a valve state may set without input from a camshaft position sensor. The technical effect of energizing all solenoids for all cylinder valves at an engine start and re-energizing the solenoids after a maximum valve duration has elapsed, all cylinder valves may be reliable placed in a desired state. Overall, valves may be set to a desired state during an engine start independent of camshaft position information. By placing valves in a target state during an engine start, a timing of cylinder fuel delivery can be optimized, engine combustion torque generation during an engine start can be improved, and overall engine startability is enhanced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.